LSM3261 LIFE FORM AND FUNCTION : protection

Dimorphism and the functional basis of claw strength in six brachyuran crabs

N. Sivasothi — Wed, 24 Oct 2007 05:33:43 GMT

Something else I mentioned today in the "Protection" lecture that I will talk about in detail during "Feeding": Schenk, S. C. & P. C. Wainwright, 2001. Dimorphism and the functional basis of claw strength in six brachyuran crabs. J. Zoology, 255 (1): 105-119. [NUS Digital Library Link]

Abstract - By examining the morphological basis of force generation in the chelae (claws) of both molluscivorous and non-molluscivorous crabs, it is possible to understand better the difference between general crab claw design and the morphology associated with durophagy. This comparative study investigates the morphology underlying claw force production and intraspecific claw dimorphism in six brachyuran crabs: Callinectes sapidus (Portunidae), Libinia emarginata (Majidae), Ocypode quadrata (Ocypodidae), Menippe mercenaria (Xanthidae), Panopeus herbstii (Xanthidae), and P. obesus (Xanthidae).
The crushers of the three molluscivorous xanthids consistently proved to be morphologically 'strong,' having largest mechanical advantages (MAs), mean angles of pinnation (MAPs), and physiological cross-sectional areas (PCSAs). However, some patterns of variation (e.g. low MA in C. sapidus, indistinguishable force generation potential in the xanthids) suggested that a quantitative assessment of occlusion and dentition is needed to understand fully the relationship between force generation and diet.
Interspecific differences in force generation potential seemed mainly to be a function of differences in chela closer muscle cross-sectional area, due to a sixfold variation in apodeme area. Intraspecific dimorphism was generally defined by tall crushers with long in-levers, though O. quadrata exhibited an extreme dimorphism suggesting that factors unrelated to a speed–strength dichotomy (e.g. sexual selection) have shaped dimorphism of that species.
It is concluded here that:
(1) the majority of interspecific claw strength variation is a function of closer muscle cross-sectional area;
(2) variation in claw morphology related to force production and transmission does have some relation to hardness of diet;
(3) claw dimorphism in many species does seem to be related to strength and speed trade-offs;
(4) factors besides molluscivory must be considered to understand claw evolution fully;
(5) a quantitative assessment of force distribution, lacking in the literature, is essential for a more complete understanding of the relationship between claw design and ecological function.

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NatGeo - Elephant hunted by 7 lions

N. Sivasothi — Wed, 24 Oct 2007 02:24:44 GMT

Dramatic footage of seven lions attacking an elephant.

Elephant VS 7 Lions - More amazing video clips are a click away

"Lions and elephants generally keep their distance from each other. But in the dry season, roughly April through October, water becomes more vital than caution, and a water hole can bring even wary adversaries into close quarters. The elephants at this water hole—by October only four inches (10 centimeters) deep and the diameter of a dining room table—squeeze other animals out, and the lions respond accordingly, eventually coming to rely on elephants for more than half their food. The first kill we saw was a six-year-old calf. With each kill the lions got bolder, attacking older calves, engaging in frontal attacks within the herd, chasing off six-ton females to get to their young. Finally, they even started attacking adults—a shocking sight never before photographed."

- National Geographic Magazine. This clip is from an article/documentary ("Preying on Giants") by the famous couple Derek and Beverly Jourbert who have spent decades in Africa filming large mammals acclimatised to their presence and soft lights. Most of us older naturalists, at least, appear to have been brought up on a diet of National Geographic magazines and films and David Attenborough documentaries. Hence the many references I highlight, which you all don;t seem to have seen. I'll se waht I can do to highlight a critical subset. Derek and Beverly Joubert were actually in Singapore in the late 90's at the old National Library. I told them I was using their "Lions of Darkness" video in class and they were very happy. Otherwise they said, they were miserable, because they were used to the African bush and the city was stressful!

Video I mentioned in class: Battle at Kruger

N. Sivasothi — Wed, 24 Oct 2007 01:53:54 GMT

"A battle between a pride of lions, a herd of buffalo, and 2 crocodiles at a watering hole in South Africa's Kruger National Park while on safari."

I had to post this up after finding out less than 10% the class has sen this. It has an excited commentary as well, adding significantly to the atmosphere. You can hear one chap with a ?South African accent ("hey guys you cannot believe what's happening"), adding the safari feel to the whole story. And a lady in the background who exclaims when the crocodile enters the fray.

But the activity that goes on is amazing with moments that defy all expectations! Its just nature at work but you can't help rooting for the buffaloes!

"I've got it on video" - well, 18.5 million views later and they are going back with Nat Geo to get the whole story! Can't wait.